Organometallics 1998, 17, 1873-1883
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Synthesis, Structures, and Properties of Strained Spirocyclic [1]Sila- and [1]Germaferrocenophanes and Tetraferrocenylsilane Mark J. MacLachlan,† Alan J. Lough,† William E. Geiger,*,‡ and Ian Manners*,† Departments of Chemistry, University of Toronto, 80 St. George Street, Toronto M5S 3H6, Ontario, Canada, and University of Vermont, Burlington, Vermont 05405-0125 Received December 6, 1997
The spirocyclic [1]ferrocenophanes [Fe(η-C5H4)2]2E (3, E ) Si; 4, E ) Ge) and Fe(η-C5H4)2Si(CH2)3 (5) have been prepared by the reaction of Fe(η-C5H4Li)2‚TMEDA (TMEDA ) tetramethylethylenediamine) with SiCl4, GeCl4, and Cl2Si(CH2)3, respectively. Single-crystal X-ray diffraction studies of 3-5 revealed that the molecules possess highly strained structures with tilt angles between the planes of the cyclopentadienyl rings of 19.4(2), 19.1(5), and 20.61(8)°, respectively. The Fe- - -Fe distances in 3 and 4 are 5.314(1) and 5.518(4) Å, and evidence for metal-metal interactions in the form of substantial redox coupling (∆E1/2 ) 0.37 V for 3 and 0.25 V for 4) is present in the cyclic voltammograms of these species. For structural comparison, the tetraferrocenylsilane [(η-C5H5)Fe(η-C5H4)]4Si (6) was prepared and was characterized by single-crystal X-ray diffraction. Cyclic voltammetry of 6 showed four reversible oxidation waves with E1/2 values of -0.03 to +0.39 V versus ferrocene; ∆E1/2 values of 0.10-0.18 V were indicative of significant metal-metal interactions. The results of Mo¨ssbauer, IR, and Raman studies of compounds 3, 4, and 6 are also discussed. Introduction The incorporation of transition metals into polymer backbones has been shown to generate materials with unusual physical and chemical properties.1,2 In this regard, ferrocene represents an appealing structural unit to include in a polymer main chain, but, until recently, high-molecular-weight poly(metallocenes) have been very rare.3-5 We have previously shown that strained silicon-bridged [1]ferrocenophanes such as 1a undergo thermal ring-opening polymerization (ROP) to afford high-molecular-weight poly(ferrocenylsilanes) (e.g. 2a).5 Recently, anionic and transition-metal-catalyzed ring-opening polymerization have also been established as facile routes to these materials.6 Ring-opened poly(metallocenes) are now known with a variety of bridging elements (for example, Ge as in 2b), and studies have shown that these materials possess intriguing physical †
University of Toronto. University of Vermont. (1) For recent examples of transition-metal-based polymeric materials, see, for example: (a) Pittman, C. U.; Carraher, C. E.; Zeldin, M.; Sheats, J. E.; Culbertson, B. M., Eds. Metal-Containing Polymeric Materials; Plenum Press: New York, 1996. (b) Altman, M.; Bunz, U. H. F. Angew. Chem., Int. Ed. Engl. 1995, 34, 569. (c) Rosenblum, M.; Nugent, H. M.; Jang, K.-S.; Labes, M. M.; Cahalane, W.; Klemarczyk, P.; Reiff, W. M. Macromolecules 1995, 28, 6330. (d) Chen, H.; Archer, R. D. Macromolecules 1995, 28, 1609. (e) Stanton, C. E.; Lee, T. R.; Grubbs, R. H.; Lewis, N. S.; Pudelski, J. K.; Callstrom, M. R.; Erickson, M. S.; McLaughlin, M. L. Macromolecules 1995, 28, 8713. (f) Buretea, M. A.; Tilley, T. D. Organometallics 1997, 16, 1507. (g) Southard, G. E.; Curtis, M. D. Organometallics 1997, 16, 5618. (2) Manners, I. Angew. Chem., Int. Ed. Engl. 1996, 35, 1602. (3) (a) Brandt, P. F.; Rauchfuss, T. B. J. Am. Chem. Soc. 1992, 114, 1926. (b) Compton, D. L.; Brandt, P. F.; Rauchfuss, T. B.; Rosenbaum, D. F.; Zukoski, C. F. Chem. Mater. 1995, 7, 2342. (4) Nugent, H. M.; Rosenblum, M.; Klemarczyk, P. J. Am. Chem. Soc. 1993, 115, 3848. (5) Foucher, D. A.; Tang, B.-Z.; Manners, I. J. Am. Chem. Soc. 1992, 114, 6246. ‡
properties.2,7-9 As cross-linking of poly(ferrocenes) is essential for many applications (e.g. for the formation of redox-active gels10), we targeted a convenient method of cross-linking materials such as 2a which would be expected to lead to enhanced mechanical properties, thermal stability, and ceramic yields. We identified the spirocyclic [1]ferrocenophanes 3 and 4 as possible cross-linking agents for poly(ferrocenes) (6) (a) Ni, Y.; Rulkens, R.; Manners, I. J. Am. Chem. Soc. 1996, 118, 4102. (b) Ni, Y.; Rulkens, R.; Pudelski, J. K.; Manners, I. Macromol. Rapid Commun. 1995, 16, 637. (c) Reddy, N. P.; Yamashita, H.; Tanaka, M. J. Chem. Soc., Chem. Commun. 1995, 2263. (7) Manners, I. Adv. Organomet. Chem. 1995, 37, 131. (8) (a) Rulkens, R.; Resendes, R.; Verma, A.; Manners, I.; Murti, K.; Fossum, E.; Miller, P.; Matyjaszewski, K. Macromolecules 1997, 30, 8165. (b) Liu, X.-H.; Bruce, D. W.; Manners, I. Chem. Commun. 1997, 289. (c) Pudelski, J. K.; Rulkens, R.; Foucher, D. A.; Lough, A. J.; Macdonald, P. M.; Manners, I. Macromolecules 1995, 28, 7301. (d) Pudelski, J. K.; Foucher, D. A.; Honeyman, C. H.; Macdonald, P. M.; Manners, I.; Barlow, S.; O’Hare, D. Macromolecules 1996, 29, 1894. (e) MacLachlan, M. J.; Aroca, P.; Coombs, N.; Manners, I.; Ozin, G. A. Adv. Mater. 1998, 10, 144. (9) (a) Nguyen, M. T.; Diaz, A. F.; Dement’ev, V. V.; Pannell, K. H. Chem. Mater. 1993, 5, 1389. (b) Tanaka, M.; Hayashi, T. Bull. Chem. Soc. Jpn. 1993, 66, 334. (c) Barlow, S.; Rohl, A. L.; Shi, S.; Freeman, C. M.; O’Hare, D. J. Am. Chem. Soc. 1996, 118, 7578. (d) Hmyene, M.; Yassar, A.; Escorne, M.; Percheron-Guegan, A.; Garnier, F. Adv. Mater. 1994, 6, 564. (10) Tatsuma, T.; Takada, K.; Matsui, H.; Oyama, N. Macromolecules 1994, 27, 6687.
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1874 Organometallics, Vol. 17, No. 9, 1998
2a and 2b, respectively. In addition, as silacyclobutanes
are also known to undergo thermal and transitionmetal-catalyzed ROP, the novel spirocyclic [1]silaferrocenophane 5 incorporating a silacyclobutane group was also expected to function as a cross-linking agent. It is noteworthy that compounds such as 3-5 may also function as volatile precursors to novel composite materials.8e In this paper, we report full details on the synthesis, characterization, and properties of all three potential cross-linking agents (3-5). We also describe the synthesis and properties of tetraferrocenylsilane 6, which provided useful comparative spectroscopic and structural data for 3. Details of the polymerization behavior of 3 and 5 and the properties of the novel crosslinked poly(ferrocene) products, which were briefly described in a recent communication,11 will be discussed in detail elsewhere.12 Results and Discussion Synthesis of the Spirocyclic [1]Ferrocenophanes 3-5 and Tetraferrocenylsilane 6. In 1975, Osborne and Whiteley reported the synthesis of 3, which was the first characterized spirocyclic [1]ferrocenophane.13 These researchers isolated 3 in very low yield (7%) from the reaction of 2 equiv of dilithioferrocene‚TMEDA (fcLi2‚TMEDA) with tetrachlorosilane, and the product was characterized by mass spectrometry, 1H NMR, and UV-vis spectroscopy. In 1980, the same group reported further spectroscopic studies (Mo¨ssbauer, 13C NMR) of the compound and a slight improvement in the yield (17%).14 Interestingly, they attempted to determine the X-ray crystal structure of 3 but reported that the crystals obtained were disordered and not suitable for X-ray diffraction studies. The synthesis of the spirocyclic [1]germaferrocenophane 4 was also reported by Osborne and co-workers via an analogous route from GeCl4.15 This species was obtained in a low, unquantified yield and was characterized by mass spectrometry, NMR, and elemental analysis. The authors indicated that the isolation and purification of 4 were frustrated by decomposition in solution. Both compounds, 3 and 4, have subsequently been investigated for protective derivatization of photoelectrochemical n-doped Si substrates.16 In our laboratory, 3 and 4 were synthesized using the same route as that described by Osborne and co(11) MacLachlan, M. J.; Lough, A. J.; Manners, I. Macromolecules 1996, 29, 8562. (12) MacLachlan, M. J.; Kulbaba, K.; Manners, I. Manuscript in preparation. (13) Osborne, A. G.; Whiteley, R. H. J. Organomet. Chem. 1975, 101, C27. (14) Osborne, A. G.; Whiteley, R. H.; Meads, R. E. J. Organomet. Chem. 1980, 193, 345. (15) Blake, A. J.; Mayers, F. R.; Osborne, A. G.; Rosseinsky, D. R. J. Chem. Soc., Dalton Trans. 1982, 2379. (16) Rosseinsky, D. R.; Osborne, A. G.; Mayers, F. R. Opt. Mater. 1996, 6, 83.
MacLachlan et al.
workers. However, the workup procedure was modified to improve the product yields. Filtration through a short column of alumina allowed any chlorinated silane/ germane species and salts to be removed. The products isolated after the filtration were stable indefinitely in solution. The yield of 3 was improved significantly (70%), but the yield of 4 was still very low ( 2σ(I)) GOF (∆/σ)max in last cycle no. of params residual electron density (e Å-3) extinction coeff abs struct param a
3
4
5
6
C20H16Fe2Si 396.12 168(2) 0.710 73 monoclinic C2/c 20.771(2) 10.304(1) 7.424(1) 100.99(1) 1559.8(3) 4 1.687 19.31 808 0.3 × 0.3 × 0.1 3.41-27.00 1748 1703 0.0331 0.0372 semiempirical 0.0747 0.0317 0.838 0.000 130 +0.395/-0.290 0.0020(2)
C20H16Fe2Ge 440.62 168(2) 0.710 73 monoclinic C2/c 21.130(9) 10.293(4) 7.437(4) 100.61(1) 1589.8(13) 4 1.841 36.73 880 0.2 × 0.2 × 0.05 3.41-26.00 1603 1562 0.0505 0.0710 semiempirical 0.1283 0.0511 0.870 0.088 106 +0.737/-0.673 0.0000(2)
C13H14FeSi 254.18 168(2) 0.710 73 monoclinic P21/n 10.603(2) 6.085(1) 17.210(2) 98.60(1) 1097.9(3) 4 1.538 14.42 528
